Heavy metals removal/stabilization from municipal solid waste incineration fly ash: a review and recent trends

Waste treatment using thermal technologies, such as incineration, leads to the production of pollutants and wastes, including fly ash (FA). Fly ash contains heavy metals (HMs) and other contaminants and can potentially pose high risks to the environment and negatively impact health and safety. Consequently, stabilizing fly ash prior to either use or landfilling is crucial. The toxicity of fly ash through heavy metal leaching can be assessed using leaching tests. The leaching rates of heavy metals primarily depend on the surrounding conditions as well as fly ash properties and metal speciation. Physical separation, leaching or extraction, thermal treatment and solidification/chemical stabilization are proposed as suitable approaches for fly ash treatment. Economic considerations, environmental concerns, energy consumption and processing times can define the efficiency and selection of the treatment approach. This review considers the latest findings and compares the advantages and shortcomings of different fly ash treatment methods with the aim of highlighting the recent advances in the field. The review concludes that the simultaneous implementation of various methods can lead to highly efficient heavy metals removal/stabilization while simultaneously taking economic and environmental considerations into account

Preliminary screening for microplastic concentrations in the surface water of the Ob and Tom Rivers in Siberia, Russia

This study characterizes the abundance and morphology of microplastics in surface water of the Ob River and its large tributary, the Tom River, in western Siberia. The average number of particles for two rivers ranged from 44.2 to 51.2 items per m3 or from 79.4 to 87.5 μg per m3 in the Tom River and in the Ob River, correspondingly. 93.5% of recovered microplastics were less than 1 mm in their largest dimension, the largest group (45.5% of total counts) consisted of particles with sizes range 0.30-1.00 mm

In-situ upgrading of Napier grass pyrolysis vapour over microporous and hierarchical mesoporous zeolites

This study presents in-situ upgrading of pyrolysis vapour derived from Napier grass over microporous and mesoporous ZSM-5 catalysts. It evaluates effect of process variables such catalyst–biomass ratio and catalyst type in a vertical fixed bed pyrolysis system at 600 °C, 50 °C/min under 5 L/min nitrogen flow. Increasing catalyst–biomass ratio during the catalytic process with microporous structure reduced production of organic phase bio-oil by approximately 7.0 wt%. Using mesoporous catalyst promoted nearly 4.0 wt% higher organic yield relative to microporous catalyst, which translate to only about 3.0 wt% reduction in organic phase compared to the yield of organic phase from non-catalytic process. GC–MS analysis of bio-oil organic phase revealed maximum degree of deoxygenation of about 36.9% with microporous catalyst compared to the mesoporous catalysts, which had between 39 and 43%. Mesoporous catalysts promoted production olefins and alkanes, normal phenol, monoaromatic hydrocarbons while microporous catalyst favoured the production of alkenes and polyaromatic hydrocarbons. There was no significant increase in the production of normal phenols over microporous catalyst due to its inability to transform the methoxyphenols and methoxy aromatics. This study demonstrated that upgrading of Napier grass pyrolysis vapour over mesoporous ZSM-5 produced bio-oil with improved physicochemical properties

Fundamental characterisation of waste and biomass for char production

Conversion of industrial waste materials to valuable resources would essentially take part in an ecologically sustainable future. There are still large amounts of undervalued biomass wastes generated from a diverse range of industries that are disposed in landfields. They have potential to produce valuable materials and fuels, such as charcoal, bio-oils and bio-gas through termal upgrading. In order to enhance the efficiency of the thermal upgrading process, comprehensive characterisation of the raw biomass materials is essential. We have developed a novel thermal characterisation method that utilises computer aided thermal analysis incorporated with a gas analyser. The method was applied on two biomass materials, wood sawdust and bagasse. The paper discusses the results obtained with the novel thermal characterisation technique.4 page(s

Technological advances of industrial biomass pyrolysis

Pyrolysis is the thermal process of decomposition of organic material under elevated temperatures and atmospheres of little or no oxygen, producing biogas, bio-oil and char. The growing interest in industrial biomass pyrolysis is the potential for upgrading of the pyrolysis bio-oils to liquid transport fuels, while the solid char, which is rich in carbon, can be used as a renewable solid fuel alternative, specialty carbon product, such as metallurgical carbon or can be blended into soils thereby sequestering carbon and improving soil quality. Industrial biomass pyrolysis processes can operate under fast or slow pyrolysis conditions, depending on the residence time and heating rate of the material in the reactor. Fast pyrolysis is characterised by rapid heating rates that are usually within the range of 1,000 to 10,000 °C/s. On a dry feed basis the yields of liquid oil from fast pyrolysis are between 50 and 80 wt% with gas and char products accounting for the remainder in approximately even proportions. Slow pyrolysis applies gradual heating rates that can be as low as several degrees per minute, where the products may range from being equally distributed amongst the solid, liquid and gas phases to producing solid and gas only. Fast pyrolysis reactor types include bubbling fluidized beds, circulating fluidized beds, rotating cone transported beds and ablative pyrolysers. Slow pyrolysis reactor designs include vacuum pyrolysers, bubbling fluidized beds, augers and heated kilns of various types. At present, most of the reactor designs have been scaled to either pilot or demonstration plant levels. The factors hindering further commercialization of biomass pyrolysis technologies are associated with the inherent limitations of the various reactors. These include raw material feed size and moisture requirements, energy efficiency, scalability restrictions, plant capital intensity and product quality. This chapter reviews and compares the strengths and weaknesses of each reactor design and elucidates the likely pathway for further development of low capital cost, scalable and energy efficient pyrolysis technology.30 page(s

Investigation of the swelling pressure development during slow pyrolysis of thermoplastic coals

Excessive pressure generated during heating and swelling of coals in coke ovens is one of the major safety concerns for the coke and steel producers. Large pressures against coke oven walls can seriously damage the ovens and reduce their life span. In the work presented here, a laboratory scale method is used to investigate swelling pressures during slow pyrolysis of thermoplastic coals with an aim in detecting the parameters which most influence this phenomenon. One of the coals chosen for this study had dangerous swelling properties with capabilities of developing excessive pressures. Results showed significant difference in the thermal behaviour of this coal when compared with the low swelling pressure coal in the temperature region of contraction of the semi-coke. Both, the high and low swelling pressure coals, were thermally investigated using series of gas analysis and long distance microscopic techniques. Results showed similarities in the amount of gas release between the two coals, especially for lower molecular weight volatiles; however, the prime difference was in their tar evolution rates and temperatures. For this purpose, the tars were collected for both coals and their blends and further analysed using matrix assisted laser desorption ionisation mass spectrometry (MALDI). Furthermore, a long distance microscopic analysis was performed on single particles under pyrolytic heating conditions revealing significant differences in the transient structural changes between both coals, which were caused by viscosity of the plastic phase and their consequent tar content